Many animals appear to have a sophisticated spatial representation of their environment (i.e., a map). The development of these maps depends on the joint abilities of discriminating novel objects and remembering their locations. A detection of novelty paradigm was used to assess mapping skills in rhesus monkeys. Socially housed monkeys in three different settings (NERPRC, UMass, NICHD Animal Center) were exposed to mapping simulations using a vertical object grid (4 rows and 4 columns for a total of 16 locations) arranged on a mesh wall of the animals' pens. Our previous research had indicated that monkeys readily responded with increased exploration to the replacement of one familiar object with a novel object, to the movement of a familiar object to a novel location, and to the swapping of two familiar objects. On most days, these changes were detected immediately. In these initial studies, monkeys were given continuous access to the grid, and only one or two changes occurred on a given day. In subsequent studies, two variations in task difficulty were examined separately. These were 1) reducing exposure to the grid by making it available to monkeys for only a two hour period each day and 2) increasing the number of grid changes per day. When grid exposure was reduced to 2 hours per day, the monkeys' responses to the grid changes (i.e., the replacement of one familiar object with a novel object and the swapping of two familiar objects) varied as a function of age. Young monkeys responded to the novel object (but not the swapped familiar objects) with increased exploration. Old monkeys did not respond to either type of grid change with increased exploratory behavior. In the second study, the number of grid changes was increased to four per day (i.e., either 4 familiar objects were replaced with novel objects or 4 familiar objects swapped locations). Under these conditions, all monkeys responded to the changes with increased exploration. This was true, even when the changes were